1. Field of the Invention
The present invention relates to new glass-ceramic materials especially for lasers or optical amplifiers, which macroscopically exhibit the advantage of glasses, namely: ease of preparation and of shaping and relatively low cost, and which microscopically exhibit the advantage of crystals, namely: high effective sections and good quantum efficiencies.
The present invention also relates to a process for the manufacture of such glass-ceramic materials.
2. Description of the Prior Art
There are already known glass-ceramic materials based on beryllium fluorides doped with rare earths, employed for their display property, as described by Auzel in Patent FR-2 077 731. On a microscopic scale these materials behave like microcrystals. However, these materials are toxic and scatter light. This scattering, which is useful in display, makes these materials unsuitable for being used in optical amplification.
Other glass-ceramic materials for laser application have been described by Rapp and Chrysochoos in J. Mat. Sci. 7 1090 (1972). They are oxide-based materials which exhibit the disadvantage that the rare-earth doping is not essentially in the crystalline phase. Overall, these glass-ceramic materials have laser properties which are inferior to those of the initial glasses (before heat treatment).
In the case of oxide-based glass-ceramic materials similar results have also been reported by Muller and Neuroth in J. Appl. Phys. 44 2315 (1973); there again the laser properties were inferior to those of the initial glasses (before heat treatment) because the rare earths were not mainly in the crystalline phase.
Mixed glass-ceramic materials based on oxide and fluorides have been described by Auzel, Morin and Pecile in Patent FR-7327 486 of 26.7.73 for use in display; they exhibit the advantage that the rare earths are only in the fluorine-containing microcrystalline phases, and this gives them a good emission efficiency. However, these materials are unsuitable for laser use because the size of the microcrystals of the order of a few micrometers makes them optically scattering.
Furthermore, glass-ceramic materials based solely on fluorides but not doped with optically active rare earths have been described, where their mechanical-properties are concerned, by Poulain and Grosdemouge in the journal Verres et Refractaires, 26 852 (1982). However, the microcrystalline phases of these glass-ceramics are of the Na.sub.7 Zr.sub.6 F.sub.31 type, that is to say are not constituted starting with the rare earth (LaF.sub.3).